This invention relates to an axle driving apparatus for independently driving the wheels of a self-propelled vehicle. In this particular invention the axle driving apparatus includes axle driving units provided with hydraulic stepless transmissions which drive single axles and which are adjacently disposed on a vehicle to independently rotate the drive wheels of such vehicle.
Axle driving units incorporating hydraulic stepless transmissions have been used to drive the axles of self-propelled vehicles for many years. Generally such units include a hydraulic pump driven by an input shaft and a hydraulic motor having an output shaft drivingly connected through a differential to a pair of oppositely disposed axles. An example of such a unit is disclosed in U.S. Pat. No. 4,914,907. However, certain self-propelled vehicles performing tasks which require tight turning capabilities and conventional hydraulic transmissions which drive a pair of axles through a differential gear assembly are not particularly suited for such purposes. Instead, vehicles have been provided with axles which are independently driven by separate axle drive units such that turns are accomplished by rotating drive wheels on opposite sides of the vehicle at different speeds and/or in different directions. Further, certain such axle driving units for independently driving single axle have incorporated hydraulic transmissions. However, such axle driving units have required housings which are of substantial height and substantial width in order to accommodate the hydraulic pump and motor and the other necessary components. Accordingly, vehicles have required large body frames in order to accommodate two such axle driving units in a side-by-side disposition, thus ruling out use of the units on many small vehicles. Further, even where a large body frame is provided, the center of gravity of the vehicle tends to be higher than is desirable for good roadability due to the height of the axle driving units and the need to dispose the prime mover of the vehicle in an elevated position to efficiently drive the units. For example, in U.S. Pat. No. 5,127,215 a dual hydrostatic drive walk-behind mower is disclosed, but it can be readily seen that the axle driving units of this mower require substantial vertical and lateral space such that a large body frame is required. It will also be noted that due to the height of the transmission housings, the engine must be disposed in an elevated position which results in the vehicle having an undesirably high center of gravity. Moreover, multiple driving belts are required to drive the input shafts of the axle driving units. (See also, U.S. Pat. Nos. 4,809,796 and 5,078,222). In U.S. Pat. No. 4,819,508, a transmission system for working vehicles is disclosed which partially solves the problem of an undesirable center of gravity by reorienting the engine such that the crank shaft is horizontally disposed. However, the axle driving mechanism still occupies substantial vertical space on the body frame, making the center of gravity undesirably high. Further, reorientation of the engine complicates the drive belt systems for driving both the axle driving units and the mower blades.
Therefore, it is an object of the present invention to provide an axle driving apparatus for independently driving axles on opposite sides of a vehicle.
It is another object of the present invention to provide an axle driving apparatus which includes side-by-side axle drive units incorporating hydraulic transmissions which require limited vertical or lateral space such that the axle driving apparatus can be used by small self-propelled vehicles, and such that vehicles utilizing such axle driving apparatus define low centers of gravity for improved roadability.
Yet another object of the present invention is to provide an axle driving apparatus having input shafts and a drive belt system which facilitates drivingly connecting the apparatus to the prime mover of the vehicle.
Still another object of the present invention is to provide an axle driving apparatus which is inexpensive to manufacture and maintain.
The present invention provides an axle driving apparatus for independently driving a pair of drive wheels on a self-propelled vehicle. The apparatus of the present invention includes axle driving units which drive a single axle, and which are selectively configured as left or right side axle driving units such that a pair of such units can be adjacently disposed in a side-by-side orientation on the body frame of the vehicle to drivingly support oppositely disposed drive wheels. Each of the axle driving units includes a housing comprising an upper half housing and a lower half housing joined to each other through a peripheral joint or junction surface. The left axle driving unit includes a single axle which projects from the left side of the housing for supporting a drive wheel on the left side of the vehicle. The right driving unit includes a single axle which projects from the right side of its housing for supporting a drive wheel on the right side of the vehicle. Whereas the axles project from opposite sides in the left and right axle driving units, in the preferred embodiment the housing is provided with bearing supports to accommodate the mounting of either a left side projecting axle or a right side projecting axle. Accordingly, the housing can be alternatively used in the construction of a left side axle driving unit or a right side axle driving unit.
In each of the axle driving units, the housing defines an enlarged region which extends perpendicular to the longitudinal axis of the operatively associated axle such that the length of the housing is greater than its width, thereby facilitating the side-by-side mounting of two axle driving units. This enlarged region accommodates the mounting of a hydraulic stepless transmission which communicates the driving force of the prime mover, or engine, of the vehicle on which the apparatus is mounted to the operatively associated axle. The transmission includes a center section which defines a pump mounting surface on which a hydraulic pump is mounted and defines a motor mounting surface on which a hydraulic motor is mounted. The center section establishes closed circuit fluid communication between the hydraulic pump and motor and is configured to advantageously dispose the pump and motor in positions displaced from the single axle such that both the height and the width of the axle driving unit is reduced. Accordingly, the axle driving units can be mounted in a lower position on the vehicle to produce a lower center of gravity and can be accommodated in a relatively narrow body frame.
The hydraulic pump includes an input shaft which projects from the housing and which is drivingly connected by a driving belt to the prime mover of the vehicle. The hydraulic motor includes an input or motor shaft drivingly connected with the operatively associated single axle. The input shaft of each of the adjacent axle driving units carries an input pulley and a single driving belt is received around the input pulleys and a drive pulley mounted on the crank shaft of the prime mover to effect rotation of the input shafts. Further, the reduced height of the axle driving units permits the input pulleys and the drive pulley to be oriented in a triangular disposition and to be aligned on a common, substantially horizontal plane. Further, it allows the prime mover to be mounted in a low position on the body frame such that the vehicle defines a low center of gravity.